Aliphatic diazo compounds : xv. formation of 1,3-dithiolane and 1,3-dithietane derivatives by the reaction of α-diazo ketones with carbon disulfide 1

Abstract

Reaction of α-diazo ketones,RCOCN 2R', with boiling carbon disulfide can give two major types of product: 2-alkylidene-1,3-dithiolan-4-one derivatives (Type A) and 4-acyl-2-alkylidene-1,-3-dithetane derivatives (type B). When R' = phenyl and R = phenyl or methyl, type A but not type B products are formed. When R' = methyl and R = phenyl or methyl, both types of product are formed; in the case where R'R' methyl, a small amount of a 4-acyl-2-alkylidene-1,3-dithiolane derivative was isolated in addition to type A and B products. When R' = H and R = phenyl, no product of type A or B could be isolated, but a 1,2,3-thiadiazole derivative was obtained in low yield. These results are interpreted in terms of reaction pathways involving electrophilic addition of carbon disulfide to the diazo carbon of the diazo ketone followed by loss of nitrogen to give an intermediate that reacts electrophilically at the diazo carbon of a second molecule of diazo ketone. It is proposed that this reaction is under kinetic control and gives rise to the less stable E -stereoisomer of the type A product, which can be converted on acid treatment to the more stable Z -stereoisomer.